Multiplex signaling



B. W. KENDALL MULTIPLEX SIGNALING Jan. 1, 1924 Filed July 19 1917 2 Sheets-Sheet l mlm #-M- im w S u Bc v...

B. W. KENDALL MULTIPLEX SIGNALING Jan. l, 1924 Filed July 19 1917 2 Sheets-Sheet- 2 atented Jan. 1, 1924.

. UNITED STATES PATENT OFFICE.

BURTON W. KENDALL, OF NEW YORK, N. Y., ASSIGNOR TO WES'IERN ELECTRIC COH- PANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

MULTIPLEX SIGNALING.

Application le July 19, 1917. Serial No. 181,581.

To all 'whom z't may comem:

Be it known that I, BURTON W.KENDALL,

7a citizen of the United States, residing at New York, in the county of New York and State of New York, have invented certain new and useful Improvements in Multiplex Signaling, of which the following is a full, clear, concise, and exact description.

This invention relates to multiplex signaling, wherein the messages are transmitted as modulations of a carrier wave. An object of the invention is to send a plurality of messages on a single carrier wave, thus obviating the necesslty of a carrier wave for each mess-age.

In the case of multiplex telegraphy, this is accomplished by uslng modulatin currents of a different frequency for eac message. These messages are detected by supplying the modulated wave to a detector, the output side of which comprises a plurality of circuits, each tuned to the frequency of one of the messages. Each message is in this way diverted to its proper channel. It is also possible for one of the signal channels to handle a telephone message. When this is done, the telegraph frequencies used must lie outside the range of the telephonie frequencies.

The invention also embodies a two-way repeating system in which the multiplex system outlined above is employed. The multiplex system may also make use of a plurality of carrier waves, each of which is modulated in accordance with a plurality of messages. In this case one side of the repeating system leads to a single high frequency line which transmits all of the modulated carrier waves. The other side of the repeating system branches into the low frequency message lines, each of which is balanced at its own frequency.

Other objects and features of the invention will appear hereinafter from the further description and the claims.

For further details of the invention, reference may be made to the drawings, in which Fig. 1 shows a multiplex repeating system for-transmitting both telephone and telegraph messages; Fi' 2 shows a similar system for han ling te egraph messages exclusively; Fig. .3 shows one t pe of modulator that may be used; and F1g. 4 illustrates a form of high frequency filter which may be employed in the system shown in Figs. 1v

out from the repeating system, the oppositeside of which comprlses the transmission llne 3, over which the signals from lines 1 and 2 are sent out as modulations of a single carrier wave. Other lines similar to lines 1 and 2 may be similarly -associated with 11ne` 3 as later described. A telgraph signal, comlng in over the line 1, energizes the relay 4, actuating the armature 5 of the same to complete a circuit through battery 6 and relay 7. The latter relay being'energized, its armatures 8 and 9 are attracted to connect the signaling generator 10 to the line 11, which leads to the input circuit of modulator 12. The line 11 includes a filter 13, whlch passes only the currents below 160 oycles to the exclusion of harmonics from the generator 10 as well as to the exclusion of telephone currents from the line 14. The filter 13 thus has two functions: (1) to purify the output of generator 10 and (2) to prevent the generator 10 from shorting out or wasting the energy of the telephone transmission. The terminations of filters 13 and 16 are such that each has a high impedance to frequencies transmitted by the other.

A telephone signal, originating in the line 2, is transferred by means of the repeating coil 15 to the line 14, which is connected to the input circuit of modulator 12. The line 14 includes the filter 16, which passes only the currents above 160 lcycles, so'that telegraph currents from the line 11 are attenuated and prevented from reaching the line 2. At the same time the filter 16 offers a.' high impedance to currents from generator 10 so that these currents are sent to the modulator 12 without being short-circuited by the filthe condenser 24 in shunt thereto for passing the high frequency currents. The high frequency currents delivered b generator 17 to the audion 20 are amplifie and modulated in accordance with the slgnaling currents coming in over the lines 11 and 14.-

'llhe modulated currents delivered by the vaudion 20 are transmitted through the high frequency filter 25 (Fig. 1) the output slde the condensers K are connected in series withthe line. 1n shunt to the line at the end section, are the branches 27 and 28, each of which includes an inductance 2L in shunt P of capacity C. rlhe two mid-shunts of this filter are similar, and each comprises an inductance L in shunt to a capacity C. 1n Fig. 1, it will be noted that the high frequency filters 29 and 30 are connected in series with the filter 25. Each of the filters 29 and 30 may, of course, have associated `therewith a modulator similar to 12, and

Frequency. K. C. L.

From the formulae given in Campbell patent No. 1,227,113, 'issued May 22, 1917, it may be readily determined that the filter associated with the source of 9,600 cycle current serves to transmit to line 3 currents of a range of frequencies from approximately 10,000 cycles down to 7,500 cycles. llt will be apparent that this filter transmits to the line 3 unmodulated currents of the frequency 9,600 cycles as produced by the carrier source, and also the lower sideband of the speech modulated carrier wave extending down in frequency from 9,600 cycles by approximately the essential speech frequency range. The frequency transmission ranges .f ,the other two filters mayA be similarly determined.

With the filters 25, 29 and 30 connected in series as shown, each filter 06ers a low impedance to currents from the other filters, so that the energy delivered by filter 25, for example, is eciently transferred to repeating coil 26 without being appreciably wasted in filters 29 and 30. Furthermore, any currents which are transferred to filter 25, for instance, from filter 29, are highly attenuated in the filter 25 and thereby pregeraete vented from reaching the modulator 12. iin case it is desired to use carrier frequencies having different values, or if it is desired to connect the filters 25, 29 and 30 in parallel, inste'ad of in series, then the proper types of filters should be substituted and their constants may be computed.. 1n case these lters are connected 1n parallel then the end sections of each filter should be spo chosen (or the filter should be so terminated) as to have a high impedance for currents delivered by the other filters, to prevent short-circuiting these other filters.

The artificial line 3 1 simulates the imedance of the line 3 and the currents from the filters 25, 29, and 30 are sent on to the line 3 without being transmitted to the line 32 as is well known in the art.

An incoming modulated wave on the line 3 is transmitted .by means of the filters 33, 34 and 35 to the proper detector and amplifier associated with one of these filters. r1`he filters 33, 34 and 35 are similar, respectively, to the filters 25, 29 and 30. 'llhe carrier wave, selectively transmitted by the filter 33, is detected and amplified at 36 by any suitable device. lf the wave supplied to the detector 36 was modulated by both a telephone and a telegraph message, then the former is transmitted through the filter 37 to the line 2 and the telegraph message, after being selectively transmitted by the filter 38, is amplified and rectified by 39, and sent by means of the relays 40 and 41 on the line 1. rllhe signal received byvrelay 4:1 is sent on to the line 1, without thereby energizing the relay l1, in the usual manner, and the telephone currents which pass through the filter 37 are transmitted to the line 2 without producing any input of energy to the modulator circuit through the line 1t. 'llhis is because the lines 1 and 2 are balanced at the message frequencies which they transmit.

The filter 38 is similar to filter 13, both transmitting telegraph currents to the exclusion of telephone currents. r1`he filter 37 is similar to filter 16, and these selectively transmit telephone currents. The drawing indicates suitable values for the capacities and inductances of filters 13 and 37; other values computed from well known formulae may be used however.

rlfhe system shown in Fig. 2 is similar to that described above, except that only telegraph messages are transmitted. lin this case the signaling generators 42, 43 and 44 may supply currents of 400 cycles, 700 cycles and 1,100 cycles, respectively. rllhese. signaling generators are associated with the modulator 45 in a manner similar to that described above in connection with Fig. 1. r1`he filters 46, 47 and 48 may be constructed as indicated at 46, and each should selectively transmit its corresponding signaling l frequency. These filters may be designed from well knownl formulae. The high frequency filters 49, 50, 51, 52, 53 and 54 are similar to the high frequency filters described above and shown in detail on Fig. 4. The low frequency filters 55, 56 and 57, connected in the out-put circuit of detector 58, should each selectively transmit its corresponding signaling frequency, the values 'of which are indicated in the drawing. The

operation of the system, shown in Fig. 2, Will be readily understood from the description of Fig. 1.

While the use of the specific forms of filters shown herein leads to good results, the invention is not restricted to the use of these specific selective circuits, and other forms of selective transmission devices may be used instead.

Although this invention has been described as ap licable to the selective operation of signa ing apparatus, it is apparent that it is adapted also for the selective operation of other mechanisms. lin general it is immaterial Whether the high frequency modulated currents are transmitted over Wires or by radio by means of transmitting and receiving antennae. Certain features of the invention, as defined in the appended claims, are capable of very general applical tion.

What is claimed is: 1'

l. A signalin system comprising a telephone line, a te egraph line, a current path, said lines being connected in parallel with respect to said path, said telephone line comprising means for attenuating telegraph currents, said telegra h line comprising means for attenuating te ephone currents, a source of carrier Waves, and means for continuously modulating said waves in accordance wit the currents supplied to said path simultaneously from both said 'telephone line and said telegraph line. v

2. A signaling system comprising a modulator having an input circuit and an output circuit, means for supplyin carrier Waves to said modulator, a plura ity of message channels associated with said input circu1t, each of said channels comprising a wave filter for attenuating currents from the other channels, anda transmission line associated with said output circuit.

3. A signalin system comprising means for supplyingt e carrier Wave to be transmitted, means for simultaneously supplying a pluralit of low frequency message currents an a single modulator adapted `t0 simultaneously modulate said Wave in accordance with said message currents.

4. A signaling system comprising means for supplying a carrier wave, means for suplying a telephone message current, means or supplying a telegraph message current, and a modulator adapted to simultaneously modulate said wave in accordance with both of said currents.

5. ln a signaling system, an electron dis-- charge device having an input circuit and an output circuit, a high-frequency generator for sup lying carrier waves to said device, a pluraity of signal channels associated with said input circuit means whereby said waves are simultaneously modulated in accordance with low frequency message currents supplied to said channels, and a transmission line associated with said output circuit.

6. A signal system comprising a telephone station and a telegraph station, low frequency transmission lines connecting each of said stations to a remote station, and means at said remote station for continuously modulating a carrier Wave simultaneously and in the same manner in accordance with both ythe 'telephone and telegraph signals transmitted over said lines.

7 A signal system comprising a telegraph station and a telephone station, low frequency lines connectin each of said stations to a remote station, a igh frequency transmission circuit at said remote station, two- Way repeating means connecting said lines and said circuit for repeating telephone and telegraph currents received overv said lines to said high frequencyv circuit as simultanelous moditicatons of the same frequency wave and for repeating to said lines, as low frequency speech currents and telegraph currents, carrier waves received from said circuit and simultaneousl modified in accordance with speech and te egraph signals.

8. A repeating system comprising a plurality of signal channels, a transmission line common to said channels, a plurality of current aths simultaneously connecting said channev s to said line, one of said paths comprising a modulator common to said channels, another of said paths comprising a detector common to said channels.

9. In a signaling system, the combination of a lurality of slgnal channels, a transmission iine common to said channels, and means between saidv channels and said line for the two-Way repeating of messages;` said means comprising, a plurality of detectors and corresponding modulators each associated with a plurality of said channels and with said line, means for supplying carrier waves to each of said modulators, means for balancing said line at all of the carrier frequencies employed, and means for balancing each of said channels at the message frequencies.

10. In combination, a modulator having an input circuit, a source of waves of carrier frequency, means connecting said source to said modulator to apply carrier Waves thereto, a plurality of low frequency signal current sources, means for simultaneouslyconnecting all of said sources to said input circuit whereby carrier waves supplied by said source of waves of carrier frequency are modulated in said modulator by currents from said plurality of low frequency signal current sources, a transmission medium, and means for impressing the modulated carrier waves from said modulator upon said transmission medium for transmission thereover.

l1. A. telegraph system comprising a Morse line, a bridge including a relay across said line, a modulator, means connected thereto for supplying carrier oscillations, a source of signal currents, and means under the control of said relay to connect said source of signal currents to said modulator.

12. ln a signaling system high frequency lselective means, demodulating means connected thereto, a low frequency selective device connected to said demodulating means, said selective device comprising a network having series inductance elements and shunt capacity elements and means connected to said device for rectifying the energy passed thereby.

13. ln combination, a selective device for transmitting current of a given. frequency to the exclusion of currents of other frequencies supplied thereto, a modulator directly connected to said device and a second selective device directly connected to said modulator and serving to exclude current of said given frequency and to transmit currents of certain other frequencies.

14. 1n combination, a plurality of selective circuits, a separate detector associated with each of said circuits, a plurality of selective devices connected to each of said detectors and a separate rectifying means connected to each of said devices,

15. rlhe method of energy distribution which comprises producing a plurality of high frequency Waves, simultaneously modulating each of saidwaves continuously by a plurality of low constant frequency Waves, preventing loss o-f energy due to interference between the low frequency Waves and simultaneously transmitting the energy of each of said modulated waves in superposed relationshi .16. The method of signaling which comprises producing a plurality of high frequency waves, continuously modulating each of said waves simultaneously in accordance with a plurality of signals, preventing interference between said plurality of signals, and simultaneously transmitting the energy of said modulated Waves in superposed relationship.

17. A telegraph system comprising a Morse line, a bridge across said line includingv a relay, a three-element electric discharge device, means connected thereto for supplying carrier oscillations, a transmission circuit connected to said device and adapted to be supplied thereby with carrier oscilla- Lamela tions, and means responsive to the operation of said relay to act upon the input circuit of said electric discharge device to control the application of said carrier oscillations to said transmission circuit.

18. The method of energy transmission which comprises simultaneously receiving a plurality of high frequency waves each modulated in accordance with a plurality of low frequency waves, separately selecting the energy of said hi h frequency Waves, detecting the energy o each of said high frequency waves to produce a plurality of low frequency components and separately rectifying each of said low frequency components.

19. A signaling system comprising a plurality of signal channels, a transmission line common to said channels, means connected between said channels and said line for the simultaneous two-Way repeating of messages, said means comprising a thermionic repeater for repeating carrier waves to said transmission line, said repeater having an output circuit connected to said line and having an input circuit, and means for controlling said input circuit in accordance with messages received simultaneously from a plurality of said signal channels.

20. A repeating system comprising a plurality of signal channels, a transmission line lcommon to said channels, a plurality of current paths connecting said channels to said line, one of said paths comprising a modulator common to said channels and another of said paths comprising a detector common to said channels and means for balancing each of said channels at the signal frequencies.

21. lin a signaling system, the combination of an electron discharge device, a plurality of input circuits adapted to impress currents of a plurality of frequencies simultaneously upon said device, and a Wave filter inserted in each input circuit to protect each input circuit from interference by the currents of the other input circuits.

22. In a signaling system, the combination of an electron' discharge device, a plu rality of input circuits adapted to impress a plurality of currents simultaneously upon said device, and a wave filter connected in each'input circuit to protect the respective input circuits from interference by currents of the frequencies impressed upon the other input circuits.

23. lln a high'frequency signaling system, the combination of a modulating device, a source of low frequency current, a source of current of different frequency and a wave filter inserted between said device and each of said sources adapted to readily transmit currents of the frequency produced by the source with which the said selecting means is connected.

' to pass currents'of the frequencies produced by their respective sources, said sources being so connected with the said modulating A device as to substantially prevent interference between the currentswhich they produce.

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25. In a high frequency signaling system, they combination of a modulating-de? vice, a circuit havin a source of current of'one frequency, a circuit having a source of current of different frequency, each of said lattery circuits having a wave filter adapted to transmit currents Aof the frequency produced b r'its particular source, and each of said latter circuits being so connected with said modulating device as to prevent current in one of said sources 4inducing currentinithe circuit of the other of said sources. f

,26. A plurality' of low frequency lines, a high frequency transmission line, means for repeating currents from each of said low frequency lines tov said high frequency line as modified carrier waves, the frequency ofthe carrier wave employed in the transmission from each of said low frequency lines being individual thereto, each of said repeating means comprising a filter having series capacity elements and shunt capacity and inductance elements, the terminations of each filter comprising shunt capacity 'and inductance elements each having reactances substantially twice those lof the corresponding shunt inductance and capacity elements between said terminations.

27. A. circuit, a plurality of channels associated therewith, means forl transferring currents of dierent frequencies between said channels and said circuit, said means comprising an individual filter connected to each of said channels the transmission ran of each filter being distinct, said filters havin terminations connectediin parallel to said circuit, the termination of each filter having a high impedance for currents of the transmission frequency range of an other filter whereby said filters do not shortcircuit each other.

28. A high frequency circuit, a pluralit of Morse lines over which Morse telegrap signals are transmitted as impulses of di rect' current, the duration of each impulse determining a character in the Morse code, such vas a 4sald Morse lines to simultaneously Irepeatv Morse signals to said circuit as highY frequency oscillations and to repeat high freuency oscillations to said Morse lines as orse signal impulses, said two way repeatdot or dash, and two way, repeatin l apparatus connecting said circuit tand "modulating apparatus ing apparatus including selective means to prevent interference between the communications of the different Morse lines.

29. A signaling system comprising a transmission line, a thermionic repeater havingv a non-linear relation between its impressed electromotive force and output current connected thereto, a source of carrier frequency waves connected to said repeater and means forv simultaneously impressing upon said repeater separate' electromotive forces representing telegraph and telephone signals.

30. The method of signaling which comprises transmitting simultaneously in both directions over a transmission channel carrier waves each of which is continuously modulated in accordance with both telegraph and telephone signals, and receiving said telegraph and telephone signals sepat rately.

232. In a composite signaling system, a

source of s eech current, a filter associated therewith or passing currents of essential voice frequencies and preventing the passage of currents lower than said essential fre- 100 uencies, a source of signaling currents of requencies outside the transmission range of said filter, a filter connected thereto for transmitting said signal currents and excluding said speech-current and'means asso- 10a ciated with said filters for controlling a high frequency wave in accordance with said voice currents and said signaling-currents.-

33. In a signaling system, a transmission line adapted to transmit high frequency currents, a translating station at one end of said line, a single modulating apparatus associated with said line at said station, means to' transmit to said translating station telephone currents and low frequency si naling currents of a different character, an means whereby said modulating apparatus may be simultaneously controlled by said telephone and other signaling currents to supply carrier currents to said'transmission line modu-v 120 latedhin, accordancewith said telephone and other"y signaling currents.

'y line, adapted to transmit high frequency currents, a translatin station at eachA end las thereof, a single mo ulating apparatus asso-v ciated with said line at one station, adeassociated 'with said line at another station, means to transmit to said first mentioned station telephone curun rents and low frequency currents of a different character, means whereby said modulating apparatus may be simultaneously controlled by said telephone and other signaling currents to supply carrier currents to said transmission line modulated in accordance with said telephone and vother signaling currents, means at said second mentioned station whereby in response to said carrier currents said demodulating apparatus supplies telephone and other low frequency signaling currents simulating the currents transmitted to said first-mentioned station, and means to separately observe said telephone and other low frequency signaling currents. p

35. lin a signaling system, a transmission line adapted to transmit high frequency currents, a plurality of transmission channels associated with one end of the line, modulating apparatus for each channel adapted to continuously supply to said line a plurality of dierent carrier frequencies characteristic of the individual channels, means to transmit to each of said channels telephone currents and low frequency signaling currents of a di'erent character, and means whereby the modulating apparatus of each channel may be simultaneously controlled by said telephone and other signaling currents to supply carrier currents to said transmission line modulated in accordance with said telephone and other signaling currents.

36. fn a signaling system, a transmission line adapted to transmit high frequency currents, a plurality of transmission channels associated with each end thereof, modulating apparatus for each channel at one end of said transmission line, said modulating apparatus being adapted to continuously supply to said line Vcarrier frequencies characteristic of each channel, demodulating apparatus for each channel at the other end of the line, means to transmit to each of said first-mentioned channels telephone currents and low frequency signaling currents of a dilerent character, means whereby themodulating apparatus of each channel may be simultaneously controlled bysaid telephone and other signaling currents to supply carrier currents to said transmission line modulated in accordance With said telephone and other signaling currents, means whereby said carrier currents are selectively transmitted to the several channels at the other end of the line, means whereby the demodulating apparatus of each channel, in response to said carrier currents, supplies telephone 'and other low frequency signaling currents simulating the currents transmitted to the corresponding channel at the originating end o the transmission line, and means to separately receive the corresponding detected telephone and other signaling currents.

madera 37. rllhe method of superposing auxiliary signaling channels upon carrier current telephone channels which conslsts 1n simultaneously transmitting a telephone current and a low frequency signaling current of a dlfferent character from the point of or1g1- nation to a common point removed therefrom, continuously modulating current of carrier frequency by both said currents simultaneously, producing thereby a carrler current continuously modulated in accordance with both the telephone current and the low frequency signaling current, ltransmitting the vmodulated current to still another point removed from said modulating S0 point and receiving said. telephone and other signaling current separately at the latter point.

38. ln a signaling system, a pair of intercommunicating stations, a signaling channel at one station, a corresponding signaling channel at the other station, a modulator in said lirst mentioned channel, a demodulator in said second mentioned channel, means to apply telephone currents to said` modulator, whereby high frequency oscillations modulated in accordance with telephone currents may 'be supplied by said modulator for transmission to the distant station, means to simultaneously apply signaling currents of a character di'erent from said telephone currents to said modulator whereby high frequency oscillations modulated in accordance with said signaling currents may be supplied by said modulator for transmission to the distantA station, means to impress the oscillations modulated in accordance with said telephone and signaling currents upon the demodulator in the corresponding channel at the distantv station, whereby said demodulator translates the modulated oscillations into the telephone and signaling currents in accordance with which said oscillations were modulated, and means forobserving said demodulated telelphone and signaling currents independ-` ent y.

39. lln a signaling system, a pair of intercommunicating stations, a plurality of signaling channels at one station, a plurality '1 15` of corresponding signaling channels at the other sta-tion, a modulator in .cach of said first mentioned' channels, a demodulator in each of said secondl mentioned channels, means to apply telephone currents to each of said modulators whereby high frequency oscillations modulated in accorda-nce with said telephone currents may be supplied by said modulators for transmission to the distant station, means tosimultaneously apply signaling currents of .afcharacter different from said telephone currents to each of said modulators whereby high frequency oscillations modulated in accordance with said signaling currents may be supplied by said modulators for transmission to the distant station, means to impress the several oscilla- .tions modulated in accordance with said rents in accordance with which the oscilla-- tions weremodulated, and meansto separately receive the demodulated telephone and signaling currents.

40. In a signaling system,.a pair of intercommunicating stations, a signaling channel at one station, a corresponding signaling channel at the other station, a modu-l lator in said first mentioned channel, means to apply telephone currents to said modulator whereby high frequency oscillations modulated in accordance with said telephone currents may be supplied by said modulator for transmission to the corresponding chan-` nel at the distant station, means to simultaneously. apply signaling currents of a character different from said telephone currents to said modulator, whereby high frequency'oscillations modulated in accordance with said signaling ycurrents may be supplied by said modulator for transmision to the corresponding channel at the distant station, and means to separately receive corresponding telephone currents and signaling currents of different character.

41. In a signaling system, a pair of intercommunicating stations, a plurality of sig naling channels at one station, a plurality of corresponding signaling channels at the otherstation, a modulator in each of said first-mentioned channels, means to apply telephone currents to each of said modulators whereby high frequency oscillations modulated in accordance with telephone currents may be supplied by said modulators for transmission to the corresponding channels at the distant station, means to simultaneously supply signaling currents of a character different from telephone currents to each of said modulators, whereby high frequency oscillations modulated in accordance with said signaling currents may be supplied by said modulators for transmission to the corresponding channels at said distant station, and means to separately receive corresponding telephone currents and signaling currents of different character.

42. In a signaling system, a pair of intercommunicating stations, a plurality of signaling channels at one station, a plurality of corresponding signaling channels at the other station, a demodulator in each of said second mentioned channels, means whereby high frequency oscillations simultaneously modulated in accordance with telephone currents and other signaling currents 'of va character different from telephone currents may be transmitted from each of said first-mentioned channels to the distant station and applied to each of said demodulators, .said demodulators functioning to translate said high frequency oscillations into the telephone currents and other signaling currents in accordance with which said oscillations were modulated, and means to separately observe said several demodulated telephone currents and other signaling currents.

- 43. In combination, a plurality of selective circuits, a separate detector associated vwith each of said circuits, a plurality of selective devices connected to each of said detectors, a separate translating device connected-to each of said last mentioned selective devices and controlled by .current selected and supplied thereby to produce signal currents of dierent wave form, and an indicating device responsive to said currents of different wave form.

44. In a high frequency signaling system, a receiving circuit comprlsing means for detecting and amplifying carrier waves modulated 1n accordance with signaling currents, a band filter adapted to `pass certain of the waves derived from said detecting and amplifying means to the exclusion of other waves, and arectifier actuated by current passing through said filter.

45. In a high frequency signaling system, a receiving circuit comprising a filter adapted to pass carrier waves modulated in accordance with signalin currents, means for detecting and ampli ying said modulated carrier waves, a band ilter'adapted to pass certain of the waves derived from said detecting and amplifying means to the exclusion of other waves, and a rectier actuated by current passing through said filter.

46. In a high frequency signaling system, areceiving circuit comprising means for detecting and amplifying carrier waves modulated in accordance with signaling currents, a band filter adapted to pass certain of the lwaves derived from said detecting and amplifying means to the exclusion of other waves, a rectifier actuated by current passing through said filter, and a relay connected to said rectifier and actuated by cur-- rent therefrom. f

47. In a high frequency signaling system, a receiving circuit comprising a filter adapted to pass carrier waves modulated in accordance with signaling currents, means for detecting and amplifying said modulated carrier Waves, a band filter adapted to pass certain of the waves derived from said detecting and amplifying means to the eX- clusion of other waves, a rectifier actuated by ,current passing through said filter, and

a relay connected to said rectifier and actuated by current therefrom.`

48. A signaling system comprising al source of lov:r frequency signaling current, a second source of low frequency signaling current of different frequency, low frequency lines connecting each of said sources to a remote station, a transmission circuitl at said remote station, two-Way repeating means connecting ,said lines and said circuit for repeating currents corresponding to the currents from both of said sources received over said-lines to said transmission circuit as simultaneous modifications of the same frequency Wave, and for repeat-v ing to said lines as low frequency currents corresponding` to currents from both said sources, carrier Waves received from said circuit, and simultaneously modified in accordance With currents corresponding to the currents from both said sources.

l 49. In a signaling system a plurality of signaling channels, a common transmission circuit, means to cause signal transmission between said channels and said circuit, a plurality of Wave ilters each having end Leraars sections including shunt impedance elements, a group circuit, some of said filters as a group having certain of their end sections connected in parallel with each other with respect tosaid group circuit, a second-group circuit, others of said filters as another group having certain of their end sections connected in series with each other and with said second group circuit and'circuit con-l nections provlding a plurality of tandem arrangements, the several .tandem arrangements having certain elements in common, and each tandem arrangement including a sitgnal channel, a filter of each of said groups o lters, a first and a second group circuit and said common transmission circuit Whereby the components ofthe signaling current fiowing in said common transmission -circuit correspond to signaling currents flowing in the respective signaling channels.

In Witness whereof, ll hereunto subscribe my name this 14th day of July A. D. 1917.

BURTON W. KENDALL. 

